diff --git a/src/main/java/rxjava/Solution.java b/src/main/java/rxjava/Solution.java
index c8657a2..a7ddf98 100644
--- a/src/main/java/rxjava/Solution.java
+++ b/src/main/java/rxjava/Solution.java
@@ -6,7 +6,7 @@ import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
 /**
- * stream.Solution involving a Sukdoku Board, a SudokuVerifier, plus some RxJava processing.
+ * stream.Solution involving a SudokuVerifier, and some RxJava processing.
 **/
 class Solution {
 	
diff --git a/src/main/java/rxjava/SudokuVerifier.java b/src/main/java/rxjava/SudokuVerifier.java
index b623eae..d01ebc8 100644
--- a/src/main/java/rxjava/SudokuVerifier.java
+++ b/src/main/java/rxjava/SudokuVerifier.java
@@ -1,46 +1,79 @@
 package rxjava;
 
-import io.reactivex.rxjava3.annotations.NonNull;
 import io.reactivex.rxjava3.core.Observable;
-import io.reactivex.rxjava3.core.Single;
 
+import java.util.List;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
 public class SudokuVerifier {
 
-	@NonNull Observable<String> digitObservable;
+
+	List<DigitField> digitFields;
 
 	public SudokuVerifier(Stream<String> digitStream) {
 		// Observable on the digit stream
-		digitObservable = Observable.fromStream(digitStream);
-	}
-
-	public boolean isSolved() {
 		AtomicInteger row = new AtomicInteger(1);
 		AtomicInteger column = new AtomicInteger(0);
-		@NonNull Observable<DigitField> digitFieldObservable = digitObservable
-			.map(digit -> digitField(row, column, digit));
-		@NonNull Observable<DigitField> filter = digitFieldObservable
-			.filter(digitField -> digitField.row == 1);
-		return isSolved(filter).blockingGet();
+		digitFields = Observable.fromStream(digitStream)
+			.map(digit -> digitField(row, column, digit))
+			.collect(Collectors.toList())
+			.blockingGet();
 	}
 
-	@NonNull Single<Boolean> isSolved(@NonNull Observable<DigitField> filter) {
-		return filter
-			.map(digitField -> digitField.digit)
-			.distinct().count()
-			.map(count -> count == 9);
+	public boolean isSolved() {
+		// Filter for 9 rows, 9 columns, 9 squares
+		return digitsInBlockFilters()
+			.map(blockFilter -> blockFilter.distinct().count().blockingGet() == 9)
+			.all(solved -> solved).blockingGet();
 	}
 
 	DigitField digitField(AtomicInteger row, AtomicInteger column, String digit) {
-		if (column.getAndIncrement() > 9) {
+		if (column.incrementAndGet() > 9) {
 			row.getAndIncrement();
 			column.set(1);
 		}
 		return new DigitField(row.get(), column.get(), digit);
 	}
 
+	Observable<Observable<String>> digitsInBlockFilters() {
+		Stream<Observable<String>> stream = Stream.of(
+			IntStream.rangeClosed(1, 9).boxed().map(row -> digitsInRowFilter(row)),
+			IntStream.rangeClosed(1, 9).boxed().map(column -> digitsInColumnFilter(column)),
+			digitsInSquareFilters()
+		).flatMap(s -> s);
+		return Observable.fromStream(stream);
+	}
+
+	Observable<String> digitsInRowFilter(Integer row) {
+		return Observable.fromStream(
+			digitFields.stream()
+				.filter(digitField -> digitField.row == row)
+				.map(digitField -> digitField.digit));
+	}
+
+	Observable<String> digitsInColumnFilter(Integer column) {
+		return Observable.fromStream(
+			digitFields.stream()
+				.filter(digitField -> digitField.column == column)
+				.map(digitField -> digitField.digit));
+	}
+
+	Stream<Observable<String>> digitsInSquareFilters() {
+		return IntStream.rangeClosed(1, 3).boxed().flatMap(
+			squareRow -> IntStream.rangeClosed(1, 3).boxed().map(
+				squareColumn -> digitsInSquareFilter(squareRow, squareColumn)));
+	}
+
+	Observable<String> digitsInSquareFilter(Integer squareRow, Integer squareColumn) {
+		return Observable.fromStream(
+			digitFields.stream()
+				.filter(digitField -> digitField.isInSquare(squareRow, squareColumn))
+				.map(digitField -> digitField.digit));
+	}
+
 	static class DigitField {
 		int row;
 		int column;
@@ -51,5 +84,12 @@ public class SudokuVerifier {
 			this.column = column;
 			this.digit = digit;
 		}
+
+		public boolean isInSquare(Integer squareRow, Integer squareColumn) {
+			return row >= squareRow * 3 - 2
+				&& row <= squareRow * 3
+				&& column >= squareColumn * 3 - 2
+				&& column <= squareColumn * 3;
+		}
 	}
 }
diff --git a/src/test/java/rxjava/SolutionTest.java b/src/test/java/rxjava/SolutionTest.java
index 8ffee72..8061222 100644
--- a/src/test/java/rxjava/SolutionTest.java
+++ b/src/test/java/rxjava/SolutionTest.java
@@ -87,6 +87,6 @@ class SolutionTest {
 	static void redirectStreams( final InputStream input, final PrintStream output, final PrintStream error ) {
 		System.setIn( input );
 		System.setOut( output );
-		System.setErr( error );
+		//System.setErr( error );
 	}
 }