# 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:

\[ BKMyx=LKyx=yy\;. \]