def METHOD_NAME(tgen):
    "Build function"
    # Create routers
    tgen.add_router("r1")
    tgen.add_router("r2")
    # r1-r2
    switch = tgen.add_switch("s1")
    switch.add_link(tgen.gears["r1"])
    switch.add_link(tgen.gears["r2"])
    # r1
    switch = tgen.add_switch("s2")
    switch.add_link(tgen.gears["r1"])
    # r2
    switch = tgen.add_switch("s3")
    switch.add_link(tgen.gears["r2"])