Def isl(x) == InjCase(x; y. true; z. false)

is mentioned by

Thm* A,B:Type, x:A+B. isl(x)  outr(x)  B	[outr_wf]
Thm* A,B:Type, x:A+B. isl(x)  outl(x)  A	[outl_wf]

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