presto-main/src/main/java/io/prestosql/sql/planner/TranslationMap.java/TranslationMap/containsSymbol
class TranslationMap:    public boolean containsSymbol(Expression expression)
    {
        if (expression instanceof FieldReference) {
            int field = ((FieldReference) expression).getFieldIndex();
            return fieldSymbols[field] != null;
        }

        Expression translated = translateNamesToSymbols(expression);
        return expressionToSymbols.containsKey(translated);
    }