-----------------------------------------------------------------------

BEGIN { FS = "[^a-z]+" }
      { for (i=1; i <= NF; i++)
            for (j=1; j <= length($i)-2; j++) {
                s = substr($i,j,3); count[s]++; word[s] = i$
            }
      }
END   { for (s in count) if (count[s]==1) print word[s])

-----------------------------------------------------------------------

{ f = "temp"
  hist[++n] = "last = " $0
  print "BEGIN {" >f
  for (i=1; i <= n; i++) print hist[i] >f
  if ($0 !~/\=/) print "print \" \" last" >f
  print "}" >f
  close(f)
  if (system("awk -f " f)) { print "error"; n--}
}

-----------------------------------------------------------------------

awk ' # acomp foo: make foo.x from foo
      { gsub(/{/, "{ xyzzy ")
        while (sub(/ xyzzy /, " xyzzy[" ++bcnt "]++; ")) ;
        print
      }
END   { print "END { for (i = 1; i <= " bcnt "; i++) " \
        "print xyzzy[i] > \"" ARGV[1] ".d\"}"}
' $1 > $1.x

-----------------------------------------------------------------------

awk ' # aprint foo: print data from foo.d with program in foo
BEGIN { while (getline < ARGV[1] ".d") > 0) count [++i] = 0+$1 }
      { gsub(/{/, " xyzzy ")
        while (sub(/ xyzzy /, "{ <<<" count[++bcnt] "... ")) '
        print
      }
' $1

-----------------------------------------------------------------------