Del

The glyph del is a triangular symbol resembling an inverted Greek delta and is represented by the Unicode character, "nabla". Its uses include: It should be noted that Del has no connection to Delta  other than visual similarity. The latter is treated as a normal identifier character in all respects.
 * In APL\360 and most other APLs, it is used to enter and exit the line editor which provides a function definition mode.
 * In Dyalog APL, NARS2000, ngn/apl, and dzaima/APL  represents the current dfn, or the function derived from the current dop, such that anonymous functions and operators may recurse.
 * In Dyalog APL,  is used to delimit tradfn members of scripted objects.
 * In APL2, APLX, and APL*PLUS, a variant glyph, consisting of a Del   overstruck with a Tilde  , is used instead of the closing   to "lock" the function definition. This prevents viewing or modifying the function's definition while still allowing the function to run. Dyalog APL instead offers the Lock Definition  system function which provides a more fine-grained management of locked behaviour.
 * In APL*PLUS,  marks a special "public comment" which can be retrieved with a dedicated system function even when the function is locked. This is also used to distinguish internal documentation from other comments.