$\mathrm{MAJ}(a,b,c) = (a\land b) \lor (b\land c) \lor (c \land a)$
$\mathrm{XOR}(a,b) = (a\land \bar b) \lor (\bar a \land b)$
$\mathrm{XOR3}(a,b,c) = \mathrm{XOR}(\mathrm{XOR}(a,b),c)$
“Solving the problem” = compute the function
“Basic steps” = AND/OR/NOT operations
$A(n,m,s)$ boolean circuit is a DAG with $n + s$ vertices
$n$ variables
$m$ outputs
$s$ size
All $n$ of the vertices are labeled as inputs $X[0],…$
The other $s$ vertices are gates AND, OR, NOT
$m$ of the gates are labeled as outputs $Y[0],…$