Past exam of the mathematics course of the University of Cambridge 2018 iii Paper 103 3 ii Solution Created 2026-10-03 Updated 2026-10-05
The implication is false. ChooseThe inequalities and the relation hold. At cell , the hook length is .
For the partition of an integer , the Hook-length formula giveswhich is divisible by . This also agrees with the degree of the standard representation of the symmetric group .
The obstruction is visible in the core of a partition: removing the horizontal rim hook of length nine leaves , which has no hook length nine and hence is the -core. Its degree is . The large hook ensures the required weight of a partition here, but the core degree is not coprime to .
Past exam of the mathematics course of the University of Cambridge 2018 iii Paper 103 3 i Solution Created 2026-10-03 Updated 2026-10-05
The equivalence is true. Write for the total size at level of the core tower of a partition , and for the corresponding total size in its quotient tower of a partition. We use the size relation and the P-adic valuation of a symmetric-group character degree from the core tower:Here is the base-p digit sum. These imply the character degree coprime to p from the core tower criterion: if , then exactly when at every level. Indeed carrying units from one position to the next decreases the sum of coefficients by ; the valuation vanishes precisely when there are no carries.
For , we also use power-core truncation of a prime-core tower: for , its core tower agrees with that of below level and is empty at every level at least . Moreover , the weight of a partition for modulus . To see the truncation, removal of a rim hook of length preserves the first -core and, under the abacus divisible-hook correspondence, becomes removal of a -hook in one quotient component. Iterating preserves all the lower cores; after all such removals, quotient level is empty.
If , the criterion gives , for , and the lower are the base- digits of . It follows that , andConversely, suppose and . Then and its lower core-tower sizes are the digits of . Quotient level of has total size . Each component there has size less than , hence is already a -core and has empty -quotient. Thus and every higher level is empty. Combined with truncation, this gives exactly the digits of , so .
ThereforeIf , necessarily and ; the -core is empty, its weight is , and the Hook-length formula shows that every degree is coprime to . Thus the equivalence holds in that boundary case too, with the empty partition having degree one.
Past exam of the mathematics course of the University of Cambridge 2022 iii Paper 160 2 b i Solution 2026-09-28
The Murnaghan–Nakayama rule states that if a permutation has a -cycle and remaining cycle type , thenwhere ranges over removable rim hooks of length and is one less than the number of rows occupied by .
Past exam of the mathematics course of the University of Cambridge 2023 iii Paper 160 2 a i Solution 2026-09-28
Power-core truncation of a prime-core tower 2026-10-05
For a prime number , integer , and , taking the -core of a partition preserves the entries of the core tower of a partition at levels and makes every level at least empty. Also the weight of a partition equals the total size at level of the quotient tower of a partition.
For the first claim, a removable rim hook of length is a bead move by on the abacus of a partition. It preserves the numbers of beads on the runners and hence the -core. Under the abacus divisible-hook correspondence, it becomes removal of a -hook in one quotient component; iteration preserves the cores at the next levels. After all -hooks are removed, every component at quotient level is empty, so every higher core level is empty as well. The weight assertion follows from iterated quotient equals a power quotient up to permutation and the size formula for the quotient of a partition.
Power-sum border-strip multiplication 2026-10-14
Multiplication of an alternant by is the sum of alternants obtained by raising one row exponent by . Equal exponents give zero. Otherwise sort the shifted beta number of a partition back into decreasing order. The resulting partition adds a size- rim hook; the number of crossed exponents is its height and supplies the determinant sign. This proves the formula through the bialternant formula. Iteration counts signed border-strip tableaux.
Skew Young diagram 2026-10-05
For diagram inclusion , the skew Young diagram consists of the cells of outside . Diagram inclusion is not the dominance order on partitions. Edge adjacency defines its connected components, and a connected skew diagram without a square is a rim hook.
With beta numbers, the staircase has set . Lowering a bead by a positive even number either hits an occupied bead or a negative position, so no even-size rim hook can be removed. The adjoint of multiplication by under the Hall inner product of symmetric functions is . The power-sum border-strip multiplication formula therefore gives zero derivative with respect to every even power sum. Since the rational symmetric-function algebra is freely generated by the power sums, the stated conclusion follows.