Ray unit
= Ray unit
{title2=$U_{\mathfrak c}=\mathcal O_K^\times\cap K_{\mathfrak c,1}^\times$}
A ray unit for a <modulus of a number field> is a unit congruent to one modulo every finite prime power in the modulus and positive at every real place in it. The group of <ray units> is the <kernel> of the <unit group> map to the <residue and signature group of a modulus>.