Yeah, proposition/variable operand types are kind of weird.

Author: bobthecow

src/Operator.php

@@ -23,7 +23,7 @@ abstract class Operator
     protected $operands = [];
 
     /**
-     * @param array $operands
+     * @param Proposition|VariableOperand ...$operands
      */
     public function __construct(...$operands)
     {
@@ -55,7 +55,10 @@ public function getOperands(): array
         return $this->operands;
     }
 
-    abstract public function addOperand($operand);
+    /**
+     * @param Proposition|VariableOperand $operand
+     */
+    abstract public function addOperand($operand): void;
 
     abstract protected function getOperandCardinality();
 }

src/Operator/PropositionOperator.php

@@ -19,6 +19,9 @@
  */
 abstract class PropositionOperator extends BaseOperator
 {
+    /**
+     * @param Proposition $operand
+     */
     public function addOperand($operand): void
     {
         $this->addProposition($operand);

src/Operator/VariableOperator.php

@@ -19,6 +19,9 @@
  */
 abstract class VariableOperator extends BaseOperator
 {
+    /**
+     * @param VariableOperand $operand
+     */
     public function addOperand($operand): void
     {
         $this->addVariable($operand);