Right Shoe

The glyph right shoe is a an oval missing its left side (resembling the top-down view of a horseshoe pointing to the right) represented by the Unicode character, "superset of". The right shoe has several uses in various dialects:
 * In SHARP APL,  is Nest when monadic and Link when dyadic.
 * In APL2, NARS2000, GNU APL, and APLX,, is Mix when monadic.
 * In Dyalog APL, dzaima/APL, and ngn/apl, , is First when monadic.
 * In all nested APLs,  is Pick when dyadic.
 * In NARS2000,  becomes Superset when used dyadically as operand of the Multiset operator.

In the context of nested APLs, monadic  is often called Disclose in symmetry of   (Left Shoe) being Enclose. However, as this name is ambiguous, the names First and Mix are to be preferred.