Allow relation symbols with parameters

Parameters must follow the relation symbol and be surrounded by braces, like so: `\rel{x}{y}{z}`.

This attempt is still brittle/broken in a few ways:
- It makes using braces in creative ways in mixfix notation ambiguous.
- It does not verify that the parameters are used in a consistent manner for each symbol. It essentially allows users to define  `a\MyRel b` and `a\MyRel{x} b` (and ones with even more parameters).
- It allows parameters for all relation symbols, even for those where it makes no sense in ordinary TeX markup, e.g. `a <{x} b`.

1 files changed, 2 insertions, 2 deletions

diff --git a/test/golden/prooffix/parsing.golden b/test/golden/prooffix/parsing.golden
index 26b2b35..2702f25 100644
--- a/test/golden/prooffix/parsing.golden
+++ b/test/golden/prooffix/parsing.golden
@@ -17,7 +17,7 @@
                         ) Positive
                         ( RelationSymbol
                             ( Symbol "=" )
-                        )
+                        ) []
                         ( ExprVar
                             ( NamedVar "x" ) :| []
                         )
@@ -44,7 +44,7 @@
                         ) Positive
                         ( RelationSymbol
                             ( Symbol "=" )
-                        )
+                        ) []
                         ( ExprVar
                             ( NamedVar "x" ) :| []
                         )