[uc_mc_semigroups]3_missing_minus_sign_in_math_example18

[shlff]

Hi @jstac , this PR adds missing - signs for some math expressions in Example 18 (The example above subsection A Necessary and Sufficient Condition of lecture uc_mc_semigroups.

The error comes from a derivation:

• e^{\lambda t (K-I)} = e^{\lambda t} e^{\lambda t K}

where e^{\lambda t} should be e^{-\lambda t}.

[jstac]

Good catch! Thanks @shlff