\boldsymbol - applies to nearly all symbols, not just letters and numbers.
{ \boldsymbol #1 }
\boldsymbol command applies bold face to nearly all symbols, not just letters and numbers.
\boldsymbol aa
\boldsymbol \alpha\alpha
\boldsymbol{a\alpha}a\alpha
\boldsymbol{a+2+\alpha+\frac{x+3}{\beta+4}}
\mathbf{a+2+\alpha+\frac{x+3}{\beta+4}}