Why do/don't these match?
Often it seems impossible to match items that seem identical. At other times we are surprised that "different" items do match. Some examples follow.
Case sensitive
'a' -: 'A' NB. No surprise here 0
Rank
1 ; ,1 NB. these look equal, but ... +-+-+ |1|1| +-+-+ 1 -: ,1 NB. a scalar vs a vector 0 1 2 3 ; ,:1 2 3 NB. these look equal, too +-----+-----+ |1 2 3|1 2 3| +-----+-----+ 1 2 3 -: ,:1 2 3 NB. a vector vs an array 0
Type
1 ; '1' NB. these look equal +-+-+ |1|1| +-+-+ 1 -: '1' NB. numeric vs literal 0
Unicode
'∇' -: '▽' NB. 16b2207 vs 16b25bd 0
Floating point tolerance
1 = 1+1e_14 1 1 = 1+1e_10 0
Contributed by BrianSchott