true 
(
M,N:T List, y:T. eq(x,y) & u.v = (M @ (y.N))) x(
eq) v (M,N:T List, y:T. eq(x,y) & u.v = (M @ (y.N)))
}
T
T
x:T. eq(x,x)
x,y:T. eq(x,y) 
eq(y,x)
x,y,z:T. eq(x,y) eq(y,z) eq(x,z)
eq) v (M,N:T List, y:T. eq(x,y) & v = (M @ (y.N)))
if eq(x,u)
true else x(eq) v fi (M,N:T List, y:T. eq(x,y) & u.v = (M @ (y.N)))
| 1 | 12. eq(x,u) = true true (M,N:T List, y:T. eq(x,y) & u.v = (M @ (y.N))) |
| 2 | 12. eq(x,u) = false x(eq) v (M,N:T List, y:T. eq(x,y) & u.v = (M @ (y.N))) |
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