submodules:

[demo] / external / gph-math

diff --git a/external/gph-math b/external/gph-math
new file mode 160000 (submodule)
index 0000000..4c82eda
--- /dev/null
+++ b/external/gph-math
@@ -0,0 +1 @@
+Subproject commit 4c82eda2dcba00a4998cfd60a13330dc793b16ca