= Lower type bound
{title2=$U<:V$}
A lower bound requires an admissible <type argument> to be a <supertype> of a specified type. In <Scala>, `[V >: U]` means $U<:V$. For an immutable <software class> covariant in `U`, a method accepting a new output value cannot consume `U` directly in a contravariant method-parameter position. Instead, `add[V >: U](x: V)` accepts a possibly wider value and returns a fresh instance parameterized by `V`. The original narrower instance remains unchanged. The <variance-position rule> and <subtyping> justify this widening; a bound alone does not authorize mutating an existing instance through a widened reference.<Scala 2.13 variance annotations specification>[Variance Annotations, lower-bound widening in the Sequence.append example]{ref}
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