# Page 197

**Location:** Chapter 21, solution to Problems 3 and 4

*Note*: additional solutions due to bird expressions equivalent to those given in the text.

## Problem 3 (c)

Besides the solution L(LL)(L(LL)), the following is also valid:

L(SM)(L(SM))\;,

## Problem 4

Besides the solution L(BKM)(L(BKM)), the following is also valid:

L(LK)(L(LK))\;,

## Short explanation

According to the first method illustrated in the Chapter, any bird A is a good solution as long as it is built according to

A = LA_1(LA_1)\;,

where all that is needed from A_1, in turn, is that it satisfies a problem-specific condition. Hence, if more than one bird A_1 is found for a certain Problem, it automatically follows that there are more than one solution for the Problem.

For Problem 3 (c), two expressions for A_1 can be found:

A_1yx=LLyx=SMyx=yy(xx)\;,

and likewise for Problem 4:

BKMyx=LKyx=yy\;.