'light-square': (i+j)%2==0 && (this.expert || !highlight),
'dark-square': (i+j)%2==1 && (this.expert || !highlight),
'highlight': !this.expert && highlight,
'light-square': (i+j)%2==0 && (this.expert || !highlight),
'dark-square': (i+j)%2==1 && (this.expert || !highlight),
'highlight': !this.expert && highlight,