 x,y:T1. Dec(x = y)
x,y:T1. Dec(x = y)
 x,y:T2. Dec(x = y)
x,y:T2. Dec(x = y)
 inl(x2) = inl(x1)
 
inl(x2) = inl(x1)  T1+T2
 T1+T2  
  inl(x2) = inl(x1)
inl(x2) = inl(x1)  T1+T2
 T1+T2
| 1 | 3.  x,y:T2. Dec(x = y) 4. x2: T1 5. x1: T1 6. x2 = x1  inl(x2) = inl(x1)  T1+T2    inl(x2) = inl(x1)  T1+T2 | 
| 2 | 3.  x,y:T2. Dec(x = y) 4. x2: T1 5. x1: T1 6.  x2 = x1  inl(x2) = inl(x1)  T1+T2    inl(x2) = inl(x1)  T1+T2 | 
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