Step
*
of Lemma
least-upper-bound-com
∀[T:Type]. ∀[R:T ⟶ T ⟶ ℙ].
  ∀[a,b,c,d:T].
    (c = d ∈ T) supposing (least-upper-bound(T;x,y.R[x;y];a;b;c) and least-upper-bound(T;x,y.R[x;y];b;a;d)) 
  supposing Order(T;x,y.R[x;y])
BY
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Latex:
Latex:
\mforall{}[T:Type].  \mforall{}[R:T  {}\mrightarrow{}  T  {}\mrightarrow{}  \mBbbP{}].
    \mforall{}[a,b,c,d:T].
        (c  =  d)  supposing 
              (least-upper-bound(T;x,y.R[x;y];a;b;c)  and 
              least-upper-bound(T;x,y.R[x;y];b;a;d)) 
    supposing  Order(T;x,y.R[x;y])
By
Latex:
Auto
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