public static Expression <Func <T, bool> > Or <T>(this Expression <Func <T, bool> > expr1, Expression <Func <T, bool> > expr2)
{
var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast <Expression>());
return(Expression.Lambda <Func <T, bool> >(Expression.Or(expr1.Body, invokedExpr), expr1.Parameters));
}