Changes

→‎Step 2: markup
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<math>\begin{array}{l}
 
<math>\begin{array}{l}
 
((x \underset{A}{\Downarrow} ~y \overset{A}{\underset{B}{\Downarrow}}) \underset{B}{\Downarrow} ~z \overset{B}{\underset{C}{\Downarrow}}) \underset{C}{\Downarrow}
 
((x \underset{A}{\Downarrow} ~y \overset{A}{\underset{B}{\Downarrow}}) \underset{B}{\Downarrow} ~z \overset{B}{\underset{C}{\Downarrow}}) \underset{C}{\Downarrow}
\\[10pt]
+
\\ \\
 
=
 
=
\\[10pt]
+
\\ \\
 
(x \underset{A}{\Downarrow}
 
(x \underset{A}{\Downarrow}
 
~ (y \overset{A}{\underset{B}{\Downarrow}}
 
~ (y \overset{A}{\underset{B}{\Downarrow}}
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\end{array}</math>
 
\end{array}</math>
 
|}
 
|}
 +
 +
Here, a notation of the form <math>x \underset{A}{\Downarrow}</math> means that <math>x\!</math> is of the type <math>A,\!</math> while a notation of the form <math>x \overset{A}{\underset{B}{\Downarrow}}</math> means that <math>x\!</math> is of the type <math>A \Rightarrow B.</math>
    
<pre>
 
<pre>
        B    C
  −
  ((x: y:): z:):
  −
      A  A B  B C
  −
  −
  =
  −
  −
        B  C  (A=>B)=>(A=>C) A=>C C
  −
  (x: (y: (z: P:            ):  ):):
  −
    A  A  B  B=>C          A=>B A C
  −
  −
Here, a notation of the form:
  −
  −
  x:
  −
    A
  −
  −
means that x is of the type A,
  −
while a notation of the form:
  −
  −
    B
  −
  x:
  −
    A
  −
  −
means that x is of the type A=>B.
  −
   
Note that the explication of P as a term K((SK)S) of
 
Note that the explication of P as a term K((SK)S) of
 
type (B=>C) => ((A=>B)=>(A=>C)) is a clue to the proof
 
type (B=>C) => ((A=>B)=>(A=>C)) is a clue to the proof
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