diff -r 000000000000 -r a5a9c433f639 src/CTT/ex/synth.ML
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/CTT/ex/synth.ML	Thu Sep 16 12:20:38 1993 +0200
@@ -0,0 +1,108 @@
+(*  Title: 	CTT/ex/synth
+    ID:         $Id$
+    Author: 	Lawrence C Paulson, Cambridge University Computer Laboratory
+    Copyright   1991  University of Cambridge
+*)
+
+writeln"Synthesis examples, using a crude form of narrowing";
+
+
+writeln"discovery of predecessor function";
+goal CTT.thy 
+ "?a : SUM pred:?A . Eq(N, pred`0, 0)	\
+\		  *  (PROD n:N. Eq(N, pred ` succ(n), n))";
+by (intr_tac[]);
+by eqintr_tac;
+by (resolve_tac reduction_rls 3);
+by (resolve_tac comp_rls 5);
+by (rew_tac[]);
+result();
+
+writeln"the function fst as an element of a function type";
+val prems = goal CTT.thy 
+    "A type ==> ?a: SUM f:?B . PROD i:A. PROD j:A. Eq(A, f ` <i,j>, i)";
+by (intr_tac prems);
+by eqintr_tac;
+by (resolve_tac reduction_rls 2);
+by (resolve_tac comp_rls 4);
+by (typechk_tac prems);
+writeln"now put in A everywhere";
+by (REPEAT (resolve_tac prems 1));
+by (fold_tac basic_defs);
+result();
+
+writeln"An interesting use of the eliminator, when";
+(*The early implementation of unification caused non-rigid path in occur check
+  See following example.*)
+goal CTT.thy 
+    "?a : PROD i:N. Eq(?A, ?b(inl(i)), <0    ,   i>)  \
+\  	          * Eq(?A, ?b(inr(i)), <succ(0), i>)";
+by (intr_tac[]);
+by eqintr_tac;
+by (resolve_tac comp_rls 1);
+by (rew_tac[]);
+uresult();
+
+(*Here we allow the type to depend on i.  
+ This prevents the cycle in the first unification (no longer needed).  
+ Requires flex-flex to preserve the dependence.
+ Simpler still: make ?A into a constant type N*N.*)
+goal CTT.thy 
+    "?a : PROD i:N. Eq(?A(i), ?b(inl(i)), <0   ,   i>)   \
+\ 	         *  Eq(?A(i), ?b(inr(i)), <succ(0),i>)";
+
+writeln"A tricky combination of when and split";
+(*Now handled easily, but caused great problems once*)
+goal CTT.thy 
+    "?a : PROD i:N. PROD j:N. Eq(?A, ?b(inl(<i,j>)), i)   \
+\  	    	           *  Eq(?A, ?b(inr(<i,j>)), j)";
+by (intr_tac[]); 
+by eqintr_tac;
+by (resolve_tac [ PlusC_inl RS trans_elem ] 1);
+by (resolve_tac comp_rls 4); 
+by (resolve_tac reduction_rls 7);
+by (resolve_tac comp_rls 10);
+by (typechk_tac[]); (*2 secs*)
+by (fold_tac basic_defs);
+uresult();
+
+(*similar but allows the type to depend on i and j*)
+goal CTT.thy 
+    "?a : PROD i:N. PROD j:N. Eq(?A(i,j), ?b(inl(<i,j>)), i) \
+\ 	    	          *   Eq(?A(i,j), ?b(inr(<i,j>)), j)";
+
+(*similar but specifying the type N simplifies the unification problems*)
+goal CTT.thy
+    "?a : PROD i:N. PROD j:N. Eq(N, ?b(inl(<i,j>)), i)	\
+\ 	    	          *   Eq(N, ?b(inr(<i,j>)), j)";
+
+
+writeln"Deriving the addition operator";
+goal Arith.thy 
+   "?c : PROD n:N. Eq(N, ?f(0,n), n)  \
+\  	        *  (PROD m:N. Eq(N, ?f(succ(m), n), succ(?f(m,n))))";
+by (intr_tac[]);
+by eqintr_tac;
+by (resolve_tac comp_rls 1);
+by (rew_tac[]);
+by (fold_tac arith_defs);
+result();
+
+writeln"The addition function -- using explicit lambdas";
+goal Arith.thy 
+  "?c : SUM plus : ?A .  \
+\  	 PROD x:N. Eq(N, plus`0`x, x)  \
+\  	        *  (PROD y:N. Eq(N, plus`succ(y)`x, succ(plus`y`x)))";
+by (intr_tac[]);
+by eqintr_tac;
+by (resolve_tac [TSimp.split_eqn] 3);
+by (SELECT_GOAL (rew_tac[]) 4);
+by (resolve_tac [TSimp.split_eqn] 3);
+by (SELECT_GOAL (rew_tac[]) 4);
+by (res_inst_tac [("p","y")] NC_succ 3);
+  (**  by (resolve_tac comp_rls 3);  caused excessive branching  **)
+by (rew_tac[]); 
+by (fold_tac arith_defs);
+result();
+
+writeln"Reached end of file.";