One White Soldier is a two candle bullish reversal candlestick pattern.

The first candle is a not short (but not necessarily long) black candle. The following does not check for the not short portion.

C1 < O1

The second candle is a not short (but necessarily long) white candle. The second candle opens above the close and below the open of the first candle and closes above the open of the first candle.

C1 < O AND O < O1 AND O1 < C

This candle forms in a downtrend. This is going to be defined here as three down closes in a row ending with the first candle.

C1 < C2 AND C2 < C3 AND C3 < C4

The resulting candlestick pattern is as follows.

C1 < O AND O < O1 AND O1 < C AND C1 < C2 AND C2 < C3 AND C3 < C4

Boolean PCFs for Candlestick Patterns