= — Equal=Y self-classifies major cells. Rows correspond to distinct cells in first-occurrence order; columns correspond to Y’s cells. Entries are equality masks.
='aba' ⍝ 2 3⍴1x 0x 1x 0x 1x 0x
X=Y tests equality, pervasively.
1 2 3=2 ⍝ 0x 1x 0x
0.3=0.1+0.2 ⍝ 1x
'abc'='b' ⍝ 0x 1x 0x