fcn playfair(text,keytable){  // text is a-z only
   keyTable,deadChr:=keytable;
   text=text.toUpper();
   text-=text - keyTable;	// remove unencodable characters
   if(deadChr=="Q") text-=deadChr; else text=text.replace("J","I");

   text=text.pump(String,T(Void.Read,1,False),
			 fcn(a,b=""){ if(a==b) a+"X"+b else a+b });
   if(text.len().isOdd) text+="Z";

   row:='wrap(c){ keyTable.index(c)/5 };
   col:='wrap(c){ keyTable.index(c)%5 };
   ltrRight:='wrap(c){ keyTable[(keyTable.index(c) + 1)%25] };
   ltrBelow:='wrap(c){ keyTable[(keyTable.index(c) + 5)%25] };
   ltrAt:='wrap(r,c) { keyTable[r*5 + c] };

   text.pump(String, Void.Read,  //-->digraph
      'wrap(a,b){
	 if((ra:=row(a))==(rb:=row(b))) return(ltrRight(a) + ltrRight(b));
	 if((ca:=col(a))==(cb:=col(b))) return(ltrBelow(a) + ltrBelow(b));
	 return(ltrAt(ra,cb) + ltrAt(rb,ca));
      })
   .pump(String,Void.Read,"".create.fp(" ")).strip(); // insert blanks
}