inc_net_euro <- seq(0, 4000, b=0.1) # 1 cent interval

# (1) part 1
fac <- rep(0.67, t=length(inc_net_euro))
# (2) part 1
inds <- which(inc_net_euro < 1000)
if (length(inds) > 0) { 
    diff_euro <- 1000 - inc_net_euro[inds]
    fac[inds] <- 0.67 + 0.001*floor(diff_euro/2) # 67 % + multiple of 2 * 0.1 %
    fac <- sapply(fac, min, 1)
}
# (2) part 2
inds <- which(inc_net_euro > 1200)
if (length(inds) > 0) { 
    diff_euro <- inc_net_euro[inds] - 1200
    fac[inds] <- 0.67 - 0.001*floor(diff_euro/2) # 67 % - multiple of 2 * 0.1 %
    fac <- sapply(fac, max, 0.65)
}
elterngeld <- fac*inc_net_euro
# (1) part 2
elterngeld <- sapply(elterngeld, min, 1800)
# (4)
elterngeld <- sapply(elterngeld, max, 300)