Jamie Walker continued his rich vein of form as Hearts secured a quickfire double over Livingston with a 1-0 win at Tynecastle.Walker fired home from close range five minutes before half-time at the second attempt after his first effort was blocked by a Livi defender - his fifth goal in six games.Moments earlier, Walker shot straight at Livi goalkeeper Darren Jamieson, who also foiled the midfielder early on.James Keatings and Prince Buaben missed chances to extend Hearts' lead before Livi had Nejc Praprotnik sent off for a second booking in the 74th minute.Genero Zeefuik and substitute Billy King squandered good opportunities towards the end but it didn't matter as Hearts - who won 3-2 at Livi last Saturday - moved 20 points clear.Callum Fordyce had gone close to giving Livi the lead in the 33rd minute but his headed from a corner was hacked off the line.