x,y:. (((x = y)))  x  y 

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ProofTree

Definitions	t  T, x:A. B(x), P  Q, P  Q, P  Q, P  Q, a  b  T ,
Lemmas	assert of eq int, not functionality wrt iff, iff functionality wrt iff, nequal wf, eq int wf, assert wf, not wf