resolve label warnings for executablebooks/sphinx-exercise#36

ctmc_lectures/generators.md

@@ -211,11 +211,13 @@ $$
 $h \to 0$ in {eq}`devlim` is the right limit.)
 
 ```{prf:example}
+:label: generators-prf-1
 If $U_t = t V$ for some fixed $V \in \linop$, then it is easy to
 see that $V$ is the derivative of $t \mapsto U_t$ at every $t \in \RR_+$.
 ```
 
 ```{prf:example}
+:label: generators-prf-2
 In {doc}`our discussion <kolmogorov_fwd>` of the Kolmogorov forward equation 
 when $S$ is finite, we introduced the derivative of a map $t
 \mapsto P_t$, where each $P_t$ is a matrix on $S$.

ctmc_lectures/kolmogorov_bwd.md

@@ -512,7 +512,7 @@ b = 10
 The calculation was done by simulating independent draws and histogramming.
 
 Try to generate the same figure using {eq}`psolq` instead, modifying code from
-{ref}`our lecture <markov_prop>` on the Markov property.
+{doc}`our lecture <markov_prop>` on the Markov property.
 ````
 
 ```{exercise}

ctmc_lectures/uc_mc_semigroups.md

@@ -153,6 +153,7 @@ The second last of these results is the Kolmogorov forward and backward equation
 The last of these results shows that we can obtain the intensity matrix $Q$ by differentiating $P_t$ at $t=0$.
 
 ```{prf:example}
+:label: uc-mc-semigroups-prf-1
 Let us consider again the Poisson process $(N_t)$ with rate $\lambda > 0$ 
 in light of the discussion above.