Everton boss David Moyes will not relax until his side is a mathematical certainty to avoid relegation from the English Premier League.A 2-1 win over Newcastle on Saturday went some way to securing Everton's future in the top flight for another year, but their realistic manager is not prepared to rest on his laurels ahead of Wednesday's clash with Birmingham City."If we had lost at Newcastle, we might have been looking over our shoulders," said Moyes, whose side lie in 10th and six points from the relegation places."And if we don't get a result in the next few home games, we might be back looking over our shoulders again. I think that is the way the league is at the moment. I think everyone is in that position.""It's not quite gone yet, and it won't be until we are far enough up the league and it is mathematically impossible."The former Preston manager is too cautious to reveal the figure he believes will ensure his side's safety."Nobody knows what the points total is. I think everybody's suggestion is that it's going to be higher than what it's been in the past," he said."If that is the case, then everybody is battling to try and get the points."Birmingham suffered a crushing defeat to West Brom on Saturday, bringing them back to earth after their Carling Cup win against Arsenal on February 27. Moyes, however, is mindful that their Wembley performance is a warning of how good they can be."I think they did great to get a result against Arsenal, and I think that showed you the level of the Premiership and how tough it is," he said.Everton captain Phil Neville has been ruled out of the game after picking up a hamstring injury in the win over Newcastle.Dutch utility man John Heitinga took his place from the bench and is set to start on Wednesday. Moyes will also be without his first-choice midfield pairing of Tim Cahill (foot) and Marouane Fellaini, with the latter ruled out of the rest of the season with ankle injury.