+{ 3 } [ "hola" "a" subsequence-starts ] unit-test
+{ f } [ "hola" "x" subsequence-starts ] unit-test
+{ 0 } [ "a" "" subsequence-starts ] unit-test
+{ 0 } [ "" "" subsequence-starts ] unit-test
+{ 0 } [ "hola" "hola" subsequence-starts ] unit-test
+{ 1 } [ "hola" "ol" subsequence-starts ] unit-test
+{ f } [ "hola" "amigo" subsequence-starts ] unit-test
+{ f } [ "hola" "holaa" subsequence-starts ] unit-test
+