)help ≢
monadic function: Z ← ≢ B (Tally)
Returns the number of elements in the first dimension of B.
dyadic function: Z ← A ≢ B (Not match)
Returns 1 if A has not the same shape and ravel as B.
But, this is a dyalog expression (which is not an ISO standard APL). Still, the symbol meaning is pretty much the same.
