$2 ......... ................... .....................$1################$2 .............. ....$1################$2 .............. ...$1################$2 ............. ..$1****************$2 ............ . .$1****************$2 ........... ... $1................$2 .......... ..... $1...............$2 ......... ....... ... .$3...... $2. $3..... .....$2.... $4........... $3.... ......$2. $4........... $3... ....... $4........... $3................ $4*********** $3................ $4########### $3**************** $3################