check for conflicting arg positions in shell builder takes account of xor subsets

Author: tclose

pydra/compose/base/task.py

@@ -604,7 +604,7 @@ def _check_arg_refs(
                 type_ = inputs[field_name].type
                 if not is_truthy_falsy(type_):
                     raise ValueError(
-                        f"Fields included in a 'xor' ({field_name!r}) must be an optional type or a"
+                        f"Fields included in a 'xor' ({field_name!r}) must be an optional type or a "
                         f"truthy/falsy type, not type {type_}"
                     )
 

pydra/compose/shell/builder.py

@@ -571,7 +571,7 @@ def remaining_positions(
     if multiple_positions := {
         k: [f"{a.name}({a.position})" for a in v]
         for k, v in positions.items()
-        if len(v) > 1 and frozenset(a.name for a in v) not in xor
+        if len(v) > 1 and not any(x.issuperset(a.name for a in v) for x in xor)
     }:
         raise ValueError(
             f"Multiple fields have the overlapping positions: {multiple_positions}"