implemented independence rule

certora/specs/ERC1155Supply.spec

@@ -1,4 +1,34 @@
 
+methods {
+    totalSupply(uint256) returns uint256 envfree
+}
+
+/// given two different token ids, if totalSupply for one changes, then
+/// totalSupply for other should not
+rule token_totalSupply_independence(method f)
+filtered {
+    f -> f.selector != _burnBatch(address,uint256[],uint256[]).selector
+      && f.selector != _mintBatch(address,uint256[],uint256[],bytes).selector
+      && f.selector != safeBatchTransferFrom(address,address,uint256[],uint256[],bytes).selector
+}
+{
+    uint256 token1; uint256 token2;
+    require token1 != token2;
+
+    uint256 token1_before = totalSupply(token1);
+    uint256 token2_before = totalSupply(token2);
+
+    env e; calldataarg args;
+    f(e, args);
+
+    uint256 token1_after = totalSupply(token1);
+    uint256 token2_after = totalSupply(token2);
+
+    assert token1_after != token1_before => token2_after == token2_before,
+        "methods must not change the total supply of more than one token";
+}
+
+
 rule sanity {
     method f; env e; calldataarg args;