Close composition

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In SHARP APL and J, a close composition is one of the operators Atop, Over, or Under, defined so that the overall result has function rank equal to the right operand. In SHARP all composition operators follow this pattern, while in J, both close and non-close forms (with a result rank of infinity, matching the definition in most APLs) are provided.

Operator SHARP J close J non-close
Atop @ @:
Over & &:
Under ¨ &. &.:


APL built-ins [edit]
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