Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_23 (partner VARCHAR, surface VARCHAR, date VARCHAR)
### Question:
What is the name of a partner that played on a hard surface on 18 April 2011?
### Answer:
SELECT partner FROM table_name_23 WHERE surface = "hard" AND date = "18 april 2011"