Find CSG for $L = \{a^ib^jc^k \mid 0 \leq i \leq j \leq k\}$
$$
\begin{align*}
S &amp;\to XABS' \mid XBS' \mid XS' \mid XAB \mid XB \mid X \mid \epsilon \\
S' &amp;\to ABCS' \mid BCS' \mid CS' \mid C \\ \\
BA &amp; \to AB \\
CA &amp; \to AC \\
CB &amp; \to BC \\ \\
XA &amp;\to aX \\
X &amp;\to Y \\
YB &amp;\to bY\\
Y &amp;\to Z \\
ZC &amp;\to cZ \\
Z &amp;\to c
\end{align*}
$$

For the intuition behind this construction see this question.