Revert "semi-simultaneous, no reverse"

This reverts commit 3ccf621.

Author: dweindl

python/sdist/amici/importers/utils.py

@@ -399,6 +399,7 @@ def smart_subs_dict(
     sym: sp.Expr,
     subs: SymbolDef,
     field: str | None = None,
+    reverse: bool = True,
 ) -> sp.Expr:
     """
     Substitutes expressions completely flattening them out. Requires
@@ -413,16 +414,27 @@ def smart_subs_dict(
     :param field:
         Field of substitution expressions in subs.values(), if applicable
 
+    :param reverse:
+        Whether ordering in subs should be reversed. Note that substitution
+        requires the reverse order of what is required for evaluation.
+
     :return:
         Substituted symbolic expression
     """
     if field is None:
-        s = {eid: expr for eid, expr in subs.items()}
+        s = [(eid, expr) for eid, expr in subs.items()]
     else:
-        s = {eid: expr[field] for eid, expr in subs.items()}
+        s = [(eid, expr[field]) for eid, expr in subs.items()]
+
+    if reverse:
+        s.reverse()
 
     with sp.evaluate(False):
-        sym = sym.subs(s, simultaneous=False)
+        for old, new in s:
+            # note that substitution may change free symbols, so we have to do
+            # this recursively
+            if sym.has(old):
+                sym = sym.xreplace({old: new})
 
     return sym