add fix for equal arrows in tikz-cd

src/math/mathfig/mathfig.pysty

@@ -42,3 +42,29 @@ __HEADER__(Math figures with TikZ / pgfplots / xy)
 \NewDocumentCommand\pullback{ O{dr} }{
     \arrow[phantom, pos=0.45]{#1}{\pullbacksymbol}
 }
+
+
+%% Fix for equal arrows in tikz, see
+% https://tex.stackexchange.com/questions/443017/equal-arrows-without-transparent-ends-possible-in-tikzcd
+
+\usetikzlibrary{decorations.markings}
+\tikzset {
+  double line with arrow/.style args=
+    { #1, #2 }
+    { decorate, decoration =
+      {
+        markings,
+        mark = at position 0 with
+          {
+            \coordinate (ta-base-1) at (0,1pt);
+            \coordinate (ta-base-2) at (0,-1pt);
+          },
+        mark = at position 1 with
+          {
+            \draw[#1] (ta-base-1) -- (0,1pt);
+            \draw[#2] (ta-base-2) -- (0,-1pt);
+          }
+       }
+     }
+}
+\tikzset{Equal/.style={-,double line with arrow={-,-}}}